The present invention relates to releasing a point-to-multipoint radio bearer for a multicast or broadcast service in a mobile terminal, and in particular, to determining the releasing of the point-to-multipoint radio bearer by checking a status of the multicast or broadcast service when a data of the multicast or broadcast service is not received for a certain period of time after the mobile terminal establishes the point-to-multipoint radio bearer and receives the data of the multicast or broadcast service.
A universal mobile telecommunication system (UMTS) is a third generation mobile communications system that has evolved from the European Global System for Mobile communications (GSM) that aims to provide an improved mobile communications service based upon a GSM core network and wideband code division multiple access (W-CDMA) wireless connection technology.
FIG. 1 illustrates an exemplary basic structure of a UMTS network. As shown in FIG. 1, the UMTS is roughly divided into a terminal 100 (mobile station, user equipment (UE), etc.), a UTRAN 120, and a core network (CN) 130. The UTRAN 120 includes one or more radio network sub-systems (RNS) 125. Each RNS 125 includes a radio network controller (RNC) 123, and a plurality of base stations (Node-Bs) 121 managed by the RNC 123. One or more cells exist for each Node B.
The RNC 123 handles the assigning and managing of radio resources, and operates as an access point with respect to the core network 130. The Node-Bs 121 receive information sent by the physical layer of the terminal 100 through an uplink, and transmit data to the terminal through a downlink. The Node-Bs 121, thus, operate as access points of the UTRAN 120 for the terminal 100. Also, the RNC 123 allocates and manages radio resources and operates as an access point with the core network 130.
Between various network structure elements, there exists an interface that allows data to be exchanged for communication therebetween.
FIG. 2 illustrates a radio interface protocol architecture (structure) between the terminal 100 and UTRAN 110 that is based upon 3GPP wireless access network technology. Here, the radio access interface protocol has horizontal layers including a physical layer, a data link layer and a network layer, and has vertical planes including a user plane for transmitting data information and a control plane for transmitting control signals. The user plane is a region to which traffic information of a user, such as voice data or Internet-protocol (IP) packets are transmitted. The control plane is a region to which control information, such as an interface of a network or maintenance and management of a call, is transmitted. In FIG. 2, protocol layers can be divided into a first layer (L1), a second layer (L2) and a third layer (L3) based upon the three lower layers of an open system interconnection (OSI) scheme that is well-known in the art of wireless (mobile) communication systems.
Each layer shown in FIG. 2 will now be described. The first layer (L1) uses various radio transmission techniques to provide information transfer service to the upper layers. The first layer (L1) is connected via a transport channel to a medium access control (MAC) layer located at a higher level, and the data between the MAC layer and the physical layer is transferred via this transfer channel. Also, between different physical layers, namely, between the respective physical layers of the transmitting side and the receiving side, data is transferred via a physical channel.
The MAC layer handles the mapping between the logical channels and the transport channels, and provides a re-allocation service of the MAC parameter for allocation and re-allocation of radio (wireless) resources. The MAC layer is connected to an upper layer called a radio link control (RLC) layer through a logical channel, and various logical channels are provided according to the type of transmitted information.
The MAC layer of the second layer (L2) provides services to a Radio Link Control (RLC) layer, which is an upper layer, via a logical channel. The RLC layer of the second layer (L2) can support reliable data transmissions, and can perform a segmentation and concatenation function on a plurality of RLC service data units (RLC SDUs) delivered from an upper layer.
A packet data convergence protocol (PDCP) layer is located at an upper layer from the RLC layer, allowing data to be transmitted effectively via a radio interface with a relatively small bandwidth through a network protocol.
The radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is only defined in the control plane, and controls the transport channels and the physical channels in relation to the configuration, the re-configuration, and the releasing of the radio bearers (RBs).
The radio bearer service refers to a service that the second layer (L2) provides for data transmission between the terminal (UE) 10 and the UTRAN 100 in order to guarantee a predetermined quality of service by the UE and the UTRAN. And in general, the radio bearer (RB) establishment refers to regulating the protocol layers and the channel characteristics of the channels required for providing a specific service, as well as respectively setting substantial parameters and operation methods.
Among the RBs, the particular RB used between the UE and the UTRAN for exchanging RRC messages or NAS messages is called a SRB (Signaling Radio Bearer). When an SRB is established between a particular UE and the UTRAN, a RRC connection exists between the UE and the UTRAN. A UE having a RRC connection is said to be in RRC connected mode, and a UE without a RRC connection is said to be in idle mode. When a UE is in RRC connected mode, the RNC determines the cell in which the UE is located (i.e., the RNC determines the UE location in units of cells), and manages that UE.
Next, multimedia broadcast/multicast service (MBMS) will be described. MBMS refers to a downlink transmission service for providing data services such as, streaming services (e.g., multimedia, video on demand, webcast) or background services (e.g., e-mail, short message services (SMS), downloading), to a plurality of terminals by employing a downlink dedicated MBMS bearer service.
MBMS can be classified into a broadcast mode and a multicast mode. The MBMS broadcast mode refers to transmitting multimedia data to all users within a broadcast area, which is a region where broadcast service is possible. In contrast, MBMS multicast mode refers to transmitting multimedia data to only a certain specified user group within a multicast area, whereby a multicast area, which is a region where multicast service is possible. Thus, an MBMS service may also be referred to as a ‘point-to-multipoint service’.
A single MBMS service can consist of one or more sessions, and MBMS data are transmitted to the plurality of terminals via an MBMS bearer service during an ongoing session.
The UTRAN uses a radio bearer (RB) to provide a MBMS bearer service to a terminal. The types of radio bearers used by the UTRAN include a point-to-point (p-t-p) radio bearer and a point-to-multipoint (p-t-m) radio bearer. Here, the point-to-point RB is a bi-directional RB that comprises a logical channel (DTCH: Dedicated Traffic CHannel) and a transport channel (DCH: Dedicated CHannel), and a physical channel (either a DPCH (Dedicated Physical CHannel) or a SCCPCH (Secondary Common Control Physical CHannel)). A point-to-multipoint RB is a uni-directional RB that comprises, as shown in FIG. 3, a logical channel (MTCH: MBMS Traffic CHannel) and a transport channel (FACH: Forward Access CHannel), and a physical channel (SCCPCH: Secondary Common Control Physical CHannel). The logical channel MTCH is configured for each MBMS service provided to a single cell, and is a channel that is used for transmitting user plane data of a particular MBMS service to a plurality of users.
The UTRAN that provides MBMS service transmits, to a plurality of terminals, a MBMS-related control message (namely, a RRC message related to MBMS service data) via a MCCH (MBMS Control CHannel). Examples of an MBMS-related message include a message that informs MBMS service data, a message that informs point-to-multipoint RB data, etc. As shown in FIG. 3, the logical channel MCCH is a point-to-multipoint downlink channel that maps to a transport channel FACH (Forward Access CHannel), which maps to a physical channel SCCPCH (Secondary Common Control Physical CHannel). For a single cell, only one MCCH exists.
A terminal wishing to receive a particular MBMS that uses a point-to-multipoint RB, first receives via the MCCH, a RRC message that includes RB data, and then the point-to-multipoint RB is established with the terminal using such RB data. Thereafter, the terminal continues to receive the physical channel SCCPCH (to which the MTCH is mapped) and obtains the data of the particular MBMS service being transmitted via the MTCH.
When one session of a particular MBMS service that uses a point-to-multipoint RB is completed, the UTRAN transmits a message that instructs the release of the point-to-multipoint bearer, via the MCCH to the terminals that are receiving the particular MBMS service. Also, the UTRAN releases the point-to-multipoint RB established at the RNC and Node B. Meanwhile, a terminal that has received the above-identified message releases the point-to-multipoint RB that had been established with the terminal for the particular MBMS service.
While a particular MBMS service is in progress, one or more sessions for that service may occur in sequence. Here, a session may be defined in various ways. For example, a session may be each complete episode of a multi-episode drama or a session may be certain portions of a sports program, such as scenes that show goals in a soccer match.
When data to be transmitted for a particular MBMS service is generated at the MBMS data source, the core network (CN) 130 informs a session start to the RNC 123. In contrast, when there is no further data at the MBMS data source to be transmitted for a particular MBMS service, the core network (CN) 130 informs a session stop to the RNC 123. Between the session start and the session stop, a data transfer procedure for the particular MBMS service can be performed. Here, only those terminals that have joined a multicast group for the MBMS service may receive data that is transmitted by the data transfer procedure.
In the above session start procedure, the UTRAN that received the session start from the core network (CN) transmits an MBMS notification to the terminals. Here, MBMS notification refers a function of the UTRAN for informing a terminal that the transmission of data for a particular MBMS service within a certain cell is impending. The UTRAN can use the MBMS notification procedure to perform a counting operation that determines the number of terminals that wish to receive a particular MBMS service within a particular cell. The counting procedure is used to determine whether the radio bearer for providing the particular MBMS service should be set as point-to-multipoint (p-t-m) or point-to-point (p-t-p). For selecting the MBMS radio bearer, the UTRAN internally establishes a threshold value. After performing the counting function, the UTRAN may set a point-to-point MBMS radio bearer if the number of terminals existing within the corresponding cell is smaller than the threshold value, and may set a point-to-multipoint MBMS radio bearer if the number of terminals existing within the corresponding cell is greater than or equal to the threshold value.
If a point-to-point radio bearer is to be set, the UTRAN allocates a dedicated logical channel to each terminal (UE) and sends the data of the corresponding service. If a point-to-multipoint radio bearer is to be set, the UTRAN uses a downlink common logical channel to send the data of the corresponding service.
In the related art, the terminals that receive a particular MBMS service upon establishing a point-to-multipoint RB, release the established point-to-multipoint RB only after they receive a message from the system instructing that the point-to-multipoint RB should be released. However, in this case, those terminals that do not receive such message due to poor radio environment conditions or operation errors, cannot properly determine when the established point-to-multipoint RB should be released.
Accordingly, if the terminal is in a temporary data reception pause state and release of the RB is prematurely performed, the terminal cannot receive any MBMS service data that was transmitted after the temporary data reception pause. Also, if the terminal could not determine whether the RB should be released and thus releasing of the RB is not performed when necessary, the terminal must continue to unnecessarily maintain the point-to-multipoint RB, which thus results in a waste of terminal resources. Namely, in the related art, the terminal cannot distinguish between a temporary data reception pause and a RB release situation, and thus cannot properly determine when the point-to-multipoint RB should be released. This results in a problem for the terminal of not being able to effectively control the operations of maintaining and releasing a radio bearer. Thus, the inventors of the present invention recognized such drawbacks of the related art and provided a solution by allowing the terminal (UE) to release a point-to-multipoint radio bearer in either an explicit manner or an implicit manner, to be explained in more detail hereafter.